Add a test for HTML entities for goog.dom.textassert, and verify the thrown values in those tests.
Add a test for HTML entities for goog.dom.textassert, and verify the thrown values in those tests.

(This was inspired by investigating the assertion code after having missed some HTML entities in cl/186648009. The assertion is working fine.)

RELNOTES: n/a

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=187388264

google/closure-library,lucidsoftware/closure-library,teppeis/closure-library,teppeis/closure-library,google/closure-library,teppeis/closure-library,lucidsoftware/closure-library,google/closure-library,lucidsoftware/closure-library,google/closure-library,lucidsoftware/closure-library,teppeis/closure-library,google/closure-library